IMPROVEMENTS TO ATTITUDE SENSING

Abstract: A system, device and method are disclosed for controlling a screen display associated with a computer, in a manner similar to joysticks, mouse type devices and the like. The present arrangement uses variable attitude data, preferably obtained from an array of mercury switches, to control the images on screen. This arrangement is particularly advantageous in wireless applications, as the data required to be transmitted is greatly reduced relative to triangulation systems.

Description: IMPROVEMENTS TO ATTITUDE SENSING Technical Field The present invention relates to sensing, and to the control of computer controlled systems, such as visual displays. Background Art Various devices have been used to control the movement of objects on computer screens, both in the context of games and of application software. Examples include various forms of joystick, mouse and trackball devices. These all provide a simulated movement on the screen in response to a change in position of mechanical parts on the device, for example movement of the ball in a mouse or trackball. These devices are ergonomically unsound and have been linked with use-related injuries. They require a reference plane to be provided by, for example, a desk top. More recently, various devices have been proposed for use in so-called virtual reality systems. These devices tend to be expensive, and rely on complex sensor arrangements arranged in a glove or the like, hard wired to a relatively powerful processor. Such devices rely on a triangulation method to locate the hand held or operated part within a limited field. It will be appreciated that the complexity and difficulty of triangulation increases drastically with the possible sensing volume, and that accordingly severe practical limitations apply to accuracy and range with such systems. US patent No. 4445011 to Hansen discloses a joystick device connected by cable to a game machine. The joystick includes 4 tilt switches adapted to detect movement of the joystick forward, backward, left and right. There is no disclosure of a system for sensing variable attitude. US Patent 4425488 to Boyd discloses a system, for use by the handicapped, for indicating the direction of movement of a cursor by tilting left, right, and the like. Again, this is sensing position in a given direction, not variable attitude. Swedish patent application No. SE-19622 discloses a system for remotely controlling a cursor via an accelerometer based device. There is no disclosure or suggestion of sensing variable attitude. It is an object of the present invention to provide a control device which is relatively simple and inexpensive, yet provides comparable or superior performance to more complex devices. Summary of Invention According to one aspect the present invention provides a control system for a computer system, comprising a remote device adapted to produce signals indicative of variable attitude, and a communications link between said remote device and a base station, said base station being adapted directly or indirectly to control a computer display by reference to signals received from said remote device. Preferably the remote device includes sensors adapted to detect at least two different attitude states in each direction of movement. Preferably said remote device includes an array of tilt sensors, said array including sensors arranged so as to sense in at least two substantially perpendicular planes, the sensors in each plane having at least two different angular positions relative to the horizon. Preferably said sensors include conductive fluid switches, most preferably mercury switches. Preferably the remote device includes processing means for receiving and performing data processing operations on outputs received from said sensors, to produce output data. Preferably the communications link is wireless, more preferably via an optical arrangement, most preferably at infra-red wavelengths. According to a further aspect the present invention provides a remote control device for a computer system including a visual display, said device being adapted to communicate with a base station, said base station being adapted directly or indirectly to control said computer display, characterised in that said remote device comprises a sensor means adapted to produce signals indicative of variable attitude of said remote device. Preferably the sensor means is adapted to detect at least two different attitude states in each direction of movement. Preferably said sensor means includes an array of tilt sensors, said array including sensors arranged so as to sense in at least two substantially perpendicular planes, the sensors for each plane having at least two different angular positions relative to the horizon. According to a further aspect the present invention provides a method of controlling a computer system including a visual display, a base station adapted to directly or indirectly control said display, and a remote device adapted to communicate with said base station, said device including sensor means adapted to produce signals indicative of variable attitude of said remote device, comprising the steps of monitoring the state of said sensor; determining whether any parameters have altered since the last monitor period; processing the altered parameters to produce a communications message; communicating said message to said base station; said base station controlling said display so as to alter the image thereon. The present invention seeks to overcome the disadvantages of the prior art by recognising that the fundamental physical measurement required in many systems is attitude, not position. What is generally required in systems driving a 2-D screen is not absolute position within a 3-D volume, but pitch and roll. This drastically reduces the amount of both information and processing required, while maintaining or increasing accuracy. Moreover, these are more intuitive variables than cartesian movement of a conventional joystick. The present invention provides control based not on manipulation of a joystick relative to a base, but rather on the orientation, or more correctly change in orientation, of the device relative to gravity. Thus, no reference plane is required for the device itself. Thus, the present invention provides control based on attitude, which is meant in the sense of the angle made by the axes of the device relative to the ground. In particular, what is sensed in not merely tilt left, right, forwards or backwards, but rather the extent and rate of such movement in the planes of measurement. This is described in the specification and claims as variable attitude. Brief Description of Drawings An illustrativθ embodiment of the present invention will now be described with reference to the accompanying figures and the appendix, in which: Appendix A is a glossary of certain terms used in the flowcharts; Figure 1 illustrates the principle of the inventive attitude sensor; Figure 2 illustrates schematically the inventive control arrangement; Figure 3 shows schematically an illustrative transmitter arrangement for the remote device; Figure 4 shows schematically an illustrative receiver base station; Figure 5 illustrates a suitable mercury switch; Figure 6 illustrates orientation of the switch in use; Figure 7 illustrates one arrangement of the switches in use; Figure 8 is a boolean diagram of one embodiment of X-axis sensing; Figure 9 illustrates suitable angles in this embodiment; Figure 10 illustrates a perspective view of the parts of an X-axis encapsulation according to the present embodiment; Figure 11 is a boolean diagram of an alternative embodiment of the X- axis sensor; Figures 12 and 13 are views similar to figures 9 and 10 for the alternative implementation; Figure 14 is a boolean diagram of one implementation of the Y-axis sensor; Figure 15 shows suitable angles for the Y-axis sensors; Figure 16 shows an encapsulation for the Y-axis sensors; Figure 17 illustrates the operation of the Y-axis array; Figure 18 illustrates an assembly incorporating the X and Y axis sensor arrays; Figure 19 is a sectional view showing one implementation as a handpiece unit; Figures 21 A and 21 B provide a flowchart describing the operation of the base unit software according to a preferred embodiment. Detailed Description The following description refers to the general principles of the present invention according to a single embodiment. It is emphasised that whilst the mercury switch array shown and described is presently preferred, the invention is not limited to this device, and alternative sensing systems and devices may be substituted. The following description refers to the general principles of the present invention utilising a particular preferred attitude sensor. However, it will be appreciated that alternative attitude sensors may be employed. It is emphasised that whilst the mercury switch array shown and described is presently preferred, the invention is not limited to this device, and alternative sensor arrangements may be provided within the present invention.This application is related to co- pending PCT applications claiming common priority by the same applicant, entitled "Sensor Data Processing" and "Attitude Sensing Array", the disclosures of which are incorporated herein by reference, and to which the reader should refer if further information is required in relation to details of software adapted to utilise the sensing array, and for further details of the preferred sensing array according to the present invention. The preferred arrangement uses a mercury switch array to sense roll and pitch of the sensing array. Throughout the specification, roll and pitch are referred sometimes to as x and y for the purposes of brevity, however it is emphasised that the parameter measured by the inventive array is attitude, in particular roll and pitch. Referring to Figure 1 , an array 10 of mercury tilt switches 11 forms the preferred basic attitude sensing device according to the present invention. The switches 11 occupy different alignments to allow for sensing of different degrees of tilt. Such switches are of conventional type, employing a glass capsule 14, a pair of contacts 12, and a small quantity of mercury 13. Tilting causes the switch to be open or closed depending upon the degree of tilt. Such switches have been experimentally determined to be very reliable in use, and very robust. An additional advantage is the inherent digital output - any given switch is either on or off, and so can be directly input to digital processors. By determining which switches are on or off, and preferably also considering which were previously on or off, a determination of attitude can be made. Preferably, the array is formed in a plastic or resin moulding 15, so that high precision is possible in the arrangement, even in a volume manufacturing situation. Any suitable technique may be used to connect the portions of the array. It will be appreciated that while mercury switches are preferred, any suitable tilt sensor could be employed in the inventive arrangement. The attitude sensor is preferably contained within a hand held device, so as to function like a joystick in a conventional system. However, the system does not require a mechanical joint as in a joystick - the reference plane is provided by gravity. It will also be understood that the inventive system is applicable to related but distinct applications, such as mouse and trackball type system replacement, and to sensing attitude based on movements of other parts of the body. For example, the inventive arrangement may be used in a virtual reality type application to sense head movements, so as to control a display and show an appropriate field of view, or to sense movements of other parts of the body. Several devices according to the present invention may be employed simultaneously, using different or common base units. However, for the sake of clarity the joystick-type device will be used to illustrate the principles of the invention. Figure 5 shows the internal physical dimensions which have been found experimentally to perform satisfactorily. The switch is preferably about 11 mm long, with an internal width of 2.4 mm, and wall thickness of about 0.8 mm. The switch is preferably substantially circular in cross section. Contacts 12 are placed at one end of the switch. Of course, other types of conductive fluid switches may be substituted if desired. The type of mercury switch illustrated is widely available commercially. The switches may be of evacuated, non- evacuated or inert gas filled type - very little difference is observed in practise according to the present invention, as there is no arcing problem as currents and voltages are low. Referring to figure 6, two possible orientations of a mercury switch are shown - what will be discussed hereafter as normal and rotated orientation, in the normal orientation as shown, the switch contacts are aligned substantially horizontally with respect to gravity, whilst in the rotated orientation they are vertically displaced. To provide the best performance in practise, the switches in the array should be positioned in the normal orientation. Figure 7 illustrates the preferred x-axis, or more properly, the roll sensor arrangement. Three mercury switches 30, 31 , 32 are arranged at various orientations on one side of the normal, corresponding to roll in one direction, and three switches 33, 34, 35 similarly on the other side, with corresponding angles from the normal on the other side. This allows for the sensing of variable attitude, as progressively more switches open as attitude is increased. Figure 8, corresponding schematically to figure 7, illustrates that as more roll is introduced, successive sensors break contact, and this is the basis for the embodiment shown in figures 9 and 10. Figure 9 shows an illustrative set of angular placements for the switches in the roll sensor. It will be understood that these are exemplary only, and that other angles may be selected if desired. Preferably, a is about 12°, b is about 350, and c is about 55< Figure 10 shows a possible encapsulation arrangement for the roll sensing array. The array is encapsulated in an enclosure formed from halves 19, 19'. Each switch is placed in a respective cavity 20, which ensures that it is in the correct angular position. Additionally, it is preferred that the shape is such as to cause the switch to assume the normal orientation. A cable duct 21 allows for electrical connection to each switch. Locating devices 22,23 allow for accurate mating of the halves of the encapsulation. The two halves19, 19' mate so as to enclose the switches. I Figures 11 to 13 show an alternative arrangement for the roll array in which instead of the contacts being normally closed and opening when tilted, the switches are normally open and close when tilted. Referring to the schematic diagram of figure 11 , switches 40 to 45 have closed contacts only as the array progressively changes in attitude.The arrangement is otherwise similar with variations, as will be apparent to those skilled in the art, to the geometry. The same angles of a, b and c are preferred as in the first arrangement Figures 14 to 17 show in more detail an arrangement for the Y-axis, or pitch , sensor. Experiment has established that only 2 switches are necessary for each sensor, rather than three as is preferred for the roll sensor. Referring to figure17, two switches 50,51 are arranged on one side of the normal in the plane, and two other 52, 53 on the other. Figure 14 shows schematically that the switches break contact once the attitude of the array passes the predefined angles. Referring to figure 15, it is preferred that a is about 150, and b is about 400 . It will be appreciated that it is possible to provide a Y-axis sensor arrangement wherein the normal state of the switches is open, by analogy to the X-axis alternative arrangement previously described with reference to figures 11 to 13. Figure 18 illustrates one way of constructing an assembled sensor array according to the present invention. All the individual sensors can be assembled into a unit suitable for incorporation into a hand held device. The units may be sized so as to stack neatly, as shown.The references to up, down etc correspond to the references on figures 16 and 10. Referring to Figure 2, in block form the overall arrangement provides for the attitude sensor to provide output to a transmitter unit, which encodes the data for transmission to a base unit, which in turn may drive a conventional joystick port or the like. It will be appreciated that the embodiments described are intended to be illustrative and not limitative of the scope of the invention. The components will be described in more detail below. This arrangement provides a fully autonomous remote unit, which is relatively low cost, yet provides a reliable high slew rate sensing mechanism. The design allows for a small number of active components. The device is microprocessor based, and does not require any initial complex alignment procedure to be carried out. It will also be understood that the mercury switch implementation enables the system to avoid wearing mechanical parts, as sensing is performed by the mercury switch based array. The present invention may be employed if desired using a hard wired link, but a wireless link is preferred, and is far superior in practical operation. The link, it is emphasised, need only send encoded attitude data. There is no triangulation involved, so that processing requirements are much reduced. Range is purely limited by the communications link - it is not confined to a defined operating space. It is important to appreciate that whilst it is possible to provide some level of performance with a switch array as shown, it is highly desirable and advantageous to provide a software based system for interpreting, processing and normalising the switch outputs. A preferred software system is described below. Further details of software operation are provided in co-pending application entitled "Sensor Data Processing", referenced above, and the reader should refer to that disclosure for further information on this aspect of the preferred implementation. Switch data, which is quantised attitudinal data values in two axes (x, y for convenience - although strictly roll, pitch), is processed by the transmitter unit. Referring to Figure 3, x and y data is received asynchronously in parallel and encoded into 3 bit binary formats by two conventional encoder i.c.s. Data may also come from keypads (preferable for certain applications) and additional indicators, e.g. fire buttons. In the illustrative embodiment, the six encoded data lines are grouped with 2 fire data outputs to form an 8 bit data bus as input to the microprocessor. Raw data is oversampled and latched before presentation to firmware embedded in the processor, which performs five major functions: 1 ) dynamic modification of pitch axis data using pre-defined modelling 2) 'intelligent' redundancy analysis and 'bandwidth' expansion 3) features enhancement e.g. Autopilot, mode switching etc 4) power management including AutoSleep (i.e. no OFF switch is used) 5) parallel to serial conversion with Pulse Position Modulation encoding. The Y-axis data is processed to provide improved practical performance. Absolute sensor movement is modified by temporal modulation algorithms , so as to reduce the need for gross movements in the Y-axis by the user. This more closely approximates to normal intuitive responses. It further provides a predictable small state change response to Y-axis movements. The processing asymmetrically synthesises pseudo-states to dynamically expand the bandwidth of sensor data. This latter occurs asynchronously to X-axis data. The processing further allows for pre-emptive response to rapid state change demands. The IR transmission protocol selected is preferably power efficient, and the encoding is provided by the microprocessor. Suitable transmitter components are commercially available. The IR transmission protocol is unlikely to provide interference with domestic appliances which are carrier based. The corresponding receiver has a wide capture angle, allowing for the minimisation of range and alignment problems in use. The hand piece is preferably designed to exploit the natural attitude sensing abilities of the bridge formed between the thumb and fingers when the hand is held as if you were about to 'shake hands.Such a design enforces a particular holding attitude, and this is further enhanced by displacement of the centre of gravity. Figure 20 provides an explanation of several terms used in relation to the software description, and a more detailed flowchart showing the operation of the remote or transmitter unit hardware is provided in figures 21 A and 21 B. An IR signal is output from the transmitter via (in this embodiment) an LED. Referring to Figure 4, the IR signal is detected by the IR phototransistor, pre-amplified, noise reduction applied (AGC, high pass filtering, pulse stretching etc.) to provide an interrupt line input for the microprocessor. The embedded receiver firmware performs four major functions: 1 ) serial to parallel conversion of Pulse Position Modulated data stream 2) error checking/data validation 3) dynamic modification of roll axis data using proprietary modelling techniques including x, y correlation 4) digital selection of appropriate resistor values to provide a synthetic proportional output. X-axis data is decoded and processed, so as to improve the operation in practice. Absolute sensor movement is modified by temporal modulation algorithms, so as to linearise apparent acceleration, and provides predictable small state change response. Pseudo-states are synthesised asymmetrically to dynamically expand the bandwidth of sensor data. This synthesis occurs asynchronously to Y-axis data. Cross-correlation of X and Y axis data is performed , so as to permit illegal state changes to be suppressed. It will be appreciated that apart from allowing for reasonable line of sight, in the IR implementation, there are not specific requirements for base station placement. This is in contrast to position fixing systems, in which a fixed position for calibration of movement is clearly essential. The base station may be readily transported or connected to another device as required. Relative to position fixing systems, the lack of triangulation calculations according to the inventive system drastically reduces the computational load on the receiver unit, with consequent cost and response time advantages, and imposes no demands on the host computer system. The output is derived from two standard analog switching i.c.'s driving an optimised resistor array. This array replicates the variable resistors normally found in proportional joysticks, but suffers from none of the usual drift problems caused by wear and tear on the resistance elements. A more detailed description of the receiver software is provided in the flowcharts. It will be appreciated that the present invention is applicable to many applications and implementations other than those described herein. The attitude sensor and sensing system are applicable to other virtual reality type applications other than that described.

Claims: CLAIMS 1. A control system for a computer system, comprising a remote device adapted to produce signals indicative of variable attitude, and a communications link between said remote device and a base station, said base station being adapted directly or indirectly to control a visual display by reference to signals received from said remote device. 2. A system according to claim 1 , wherein the remote device includes sensors adapted to detect at least two different attitude states in each direction of movement. 3. A system according to claim 2 or claim 3, wherein said remote device includes an array of tilt sensors, said array including sensors arranged so as to sense in at least two substantially perpendicular planes, the sensors in each plane having at least two different angular positions relative to the horizon. 4. A system according to claim 3, wherein said sensors include conductive fluid switches. 5. A system according to claim 4, wherein said sensors comprise mercury switches. 6. A system according to any one of claims 2 to 5, wherein the remote device includes processing means for receiving and performing data processing operations on outputs received from said sensors, to produce output data. 7. A system according to claim 6, wherein said processing means further encodes said output data for communication to said base station. 8. A system according to any one of the preceding claims, wherein the communications link is wireless. 9. A system according to claim 8, wherein the link is via an optical arrangement. 10. A system according to claim 9, wherein the link operates at infra-red wavelengths. 11. A remote control device for a computer system including a visual display, said device being adapted to communicate with a base station, said base station being adapted directly or indirectly to control said computer display, characterised in that said remote device comprises a sensor means adapted to produce signals indicative of variable attitude of said remote device. 12 . A device according to claim 11, wherein the sensor means is adapted to detect at least two different attitude states in each direction of movement. 13. A device according to claim 11 or claim 12, wherein said sensor means includes an array of tilt sensors, said array including sensors arranged so as to sense in at least two substantially perpendicular planes, the sensors for each plane having at least two different angular positions relative to the horizon. 14. A device according to claim 13, wherein said sensors include conductive fluid switches. 15. A device according to claim 14, wherein said sensors comprise mercury switches. 16. A device according to any one of claims 12 to 15, including processing means for receiving and performing data processing operations on outputs received from said sensor means, to produce output data. 17. A device according to claim 16, wherein said processing means further encodes said output data for communication to said base station. 18. A method of controlling a computer system including a visual display, a base station adapted to directly or indirectly control said display, and a remote device adapted to communicate with said base station, said device including sensor means adapted to produce signals indicative of variable attitude of said remote device, comprising the steps of monitoring the state of said sensor; determining whether any parameters have altered since the last monitor period; processing the altered parameters to produce a communications message; communicating said message to said base station; said base station controlling said display so as to alter the image thereon. APPENDIX A Several terms are used in the accompanying figures which have a specific meaning within this context. A brief explanation of them follows. X, Y these are aliases for the co-ordinates of motion roll, pitch Oversample the process of looking at input values multiple times with a time delay between samples ... typically employed to lower indeterminacy errors and/or debounce mechanical switches Features AutoPilot, Console mode GeoLoc mode - these modes do not directly modify X or Y data, but merely alter the nature of operation of the device, i.e. AutoPilot freezes the current attitude until released. Console mode disconnects Geoloc sensors and limits output to digital keypad only. GeoLoc mode allows proportional attitude sensing as well as digital keypad. DABAD the dynamic modelling modules; they operate on both axes independently (asynchronously), alter their action depending on the relative direction of motion (bi-phasic) and behave differently depending on motion towards or away from the centre null position (asymmetrical), hence DUAL ASYNCHRONOUS BI-PHASIC ASYMMETRICAL DYNAMICS. Synthesise generate pseudo' states .. i.e. interim attitudinal states for which there are no physical sensor states. This is used to increase the available data bandwidth required for effective modelling to magnify absolute motion in Υ' and sensitivity in 'X'. Sticky Moments delayed transitions from state to state (real or pseudo) in order to give the appearance of a smooth movement of the cursor when the actual data is quite 'lumpy'. Temporary Moduiationthe technical terminology for the style of process utilised when 'sticky moments' are taking place. RCX, TRX abbreviations of Receiver / Transmitter Mode #1, #2, #3, #4 Levels of redundancy / Power conservation AutoSleep device in mode # ('OFF'), awaiting user to initiate re-start PPM Pulse Position Modulation: a transmission format based on the concept of identifying transmitted values by the time interval (mark-space ratio) which separates them. History data values which have been previously encountered and saved for later use in analysis processes and modelling heuristics

Inventors: WALKER PETER JOSEPH MICHAEL, WALKER, PETER, JOSEPH, MICHAEL
Applicants: BALLAR PTY LTD, WALKER PETER JOSEPH MICHAEL, BALLAR PTY. LTD., WALKER, PETER, JOSEPH, MICHAEL
Application year: 1994
Main classification: G06F3
IPC codes: G01C9, G06F3